1. Field of the Invention
The present invention relates to an axle driving apparatus contained in a housing comprising a hydrostatic transmission ("HST"), axles, and a transmitting mechanism connecting the HST to the axles. Specifically, a differential locking system is provided on a differential gear unit of the transmitting mechanism for the axles.
2. Description of the Related Art
An axle driving apparatus contained in a housing, comprising an HST, axles and a transmitting mechanism connecting the HST and the axles with each other is well-known. The transmitting mechanism of such an axle driving apparatus includes a differential gear unit for differentially rotating the left and right axles. The differential gear unit may include a differential locking system restricting the differential rotation of the axles so as to enable a vehicle having the axle driving apparatus to travel easily on soft terrain.
The conventional differential locking system is constructed such that a differential casing, which includes differential pinions and differential side gears fixed to a differential input gear (a ring gear), engages with one of the left and right axles, thereby making the axles rotate integrally. A conventional differential locking system comprises a shifter, which is not relatively rotatable and is axially slidably disposed around the axle and can engage with the differential casing, and an arm, which is rotatably disposed at the outside of the housing of the axle driving apparatus. When the arm is rotated by means of a differential locking operational tool like a lever or a pedal, the shifter slides on the axle so that the differential casing engages with or disengages from the axle.
In such a construction of a conventional differential locking system, the differential casing requires a large space and is necessarily located apart from the differential input gear, thereby expanding the housing size. Modifying such a construction such that the differential input gear and one of the left and right axles engages with each other through pins or the like, without the differential casing, causes the differential input gear to lean at heavy loads due to insufficient supporting strength. Accordingly, the toothed portion of the differential input gear generates eccentric friction, thereby reducing the durability and longevity of the differential gear unit. Thus, a compact differential locking system made without a differential casing which still prevents leaning of the differential input gear is desired.
Furthermore, in a conventionally constructed differential locking system, the arm which interlocks with the shifter includes a rotary shaft, which rotates together with the arm, disposed in the housing. A changing mechanism is therefore required which changes the rotation of the rotary shaft into the sliding movement of the shifter. The changing mechanism comprises, for example, a cam means, which is complicated and increases the number of pans required. Thus, it is desirable to simplify the changing mechanism and to enable the shifter to be shifted steadily.
Also, it is desirable to dispose the arm interlocking with a pedal or a lever at the circumference of the housing such that it does not interfere with the members of the HST which project from or into the housing, such as the input shaft and speed changing shaft.